1. Field of the Invention
This invention relates to an ignition controlling apparatus of a multi-cylinder internal combustion engine, especially to an ignition controlling apparatus which distinguishes cylinders to be ignited of the internal combustion engine, and carries out ignition controlling of the distinguished cylinders.
2. Description of Related Art
FIG. 1 is a block diagram showing a construction of a conventional ignition controlling apparatus of a low voltage distribution method with three ignition coils which is applied in six-cylinder internal combustion engine (hereinafter to be called engine). In the figure, reference numeral 1 is a disc-like first rotor which is driven by a cam shaft (not shown) of the engine, and rotates in the direction of an arrow. On the peripheral surface of the first rotor 1, six pieces to be detected 2, 2 . . . having same circumferential lengths are fixed with equal intervals from the one to the next. At the position which opposes to the peripheral surface of the first rotor 1, there is provided an angle detector 3 which employs a proximity switch, for example. The angle detector 3 detects the pieces to be detected 2, 2 . . . and outputs a first pulse signal SGT of a waveform shown in FIG. 2(a), which indicates a referential position .theta.r of rotational direction of each cylinder. The first pulse signal SGT is the one whose period and width are constant when rotating speed is constant, and the angle detector 3 outputs six pulses which falls at 75.degree. before top dead center (B75.degree.) of each cylinder and rises at 5.degree. before top dead center (B5.degree.) thereof when the engine rotates once. And the cam shaft drives a second rotor 4 in the direction shown by an arrow in the same way as the first rotor 1. On the peripheral surface of the second rotor 4, two kinds of pieces to be detected 5, 5' . . . whose circumferential lengths are different from each other are fixed two by two. The pieces to be detected 5, 5' are fixed to be opposed to each other, the circumferential length of the piece 5' being shorter than that of the piece 5. In addition, intervals between the piece 5 and the piece 5' are not equal, that is, one being longer than the other. At the position which opposes to the peripheral surface of the second rotor 4, there is provided a cylinder detector 6 which employs a proximity switch, for example. The cylinder detector 6 detects the pieces to be detected 5, 5' . . . and outputs a second pulse signal SGC of a waveform shown in FIG. 2(b). The waveform of the second pulse signal SGC corresponds to the circumferential lengths and allocated positions of the pieces to be detected 5, 5' . . . . That is, the width of the detected pulse of the piece to be detected 5' is shorter than that of the piece to be detected 5, one pulse interval being shorter than the other pulse interval. The first pulse signal SGT from the angle detector 3 is outputted respectively to a period measuring unit 7 for measuring a period T of the first pulse signal SGT, a timer 10 and a cylinder distinguishing unit 11 to be described later. The second pulse signal SGC from the cylinder detector 6 is given to the cylinder distinguishing unit 11 which outputs a cylinder distinguishing signal (to be described later) for distinguishing specific cylinders to be ignited next according to a phase between the first pulse signal SGT and the second pulse signal SGT.
The period T outputted from the period measuring unit 7 is given to an angle-time calculating unit 9. A target ignition timing calculating unit 8, which calculates a target ignition timing .theta. according to engine information such as engine speed, boost pressure and so on, gives the target ignition timing (indicated by .theta.) to the angle-time calculating unit 9. The angle-time calculating unit 9 calculates a time t.sub.a corresponding to an angle from the referential position .theta.r to the target ignition timing .theta. by the equation t.sub.a =(.theta.r-.theta.).multidot.T/120 on the basis of the period T and target ignition timing .theta.. The calculated time t.sub.a is given to a timer 10. The timer 10 outputs an ignition controlling signal afer the time t.sub.a passes from the time when the engine has reached the referential position .theta., with the position of the falling edge of the first pulse signal SGT given from the angle detector 3 being the referential position .theta.. The ignition controlling signal outputted from the timer 10 and the cylinder distinguishing signal outputted from the cylinder distinguishing unit 11 are given to a distributor 12. The distributor 12 distributes the ignition controlling signal to three transistors 14a, 14b, and 14c corresponding to the cylinder distinguishing signal. The transistors 14a, 14b, and 14c switches on/off ignition coils 13a, 13b, and 13c according to the distributed ignition controlling signal, thereby carrying out an ignition operation.
FIG. 3 is a drawing explaining the method for distinguishing cylinders.
Here, n indicates a detecting timing of this time of the angle detector 3. In the ignition controlling apparatus of the aforesaid conventional internal combustion engine, as shown in FIG. 3, by sampling the second pulse signal SGC at the rising edge (B5.degree.) and falling edge (B75.degree.) of the first pulse signal SGT, the level of "0" or "1" thereof is judged, then cylinders to be ignited next are distinguished. That is, 1 and 4 cylinders are distinguished when B5.degree.="0", B75.degree.="0", 2 and 5 cylinders when B5.degree.="1", B75.degree.="1", and 3 and 6 cylinders when B5.degree.="0", B75.degree.="1".
When noise is superimposed in the first pulse signal SGT and the second pulse signal SGC shown in FIG. 2, normal cylinder distinguishing is not carried out, thereby wrong cylinders being sometimes ignited. In this case, there is a problem that engine is damaged.